Welded boiler drum



Dec. 24, 1935. L. G. HALLER 2,025,049

WELDED BOILER DRUM Filed Dec. 13, 1933 (mun; J

EHLLL EHLLL mm 4 y +-mfls L g N {UTE INVENTOR v ATTORNEY! Patented Dec. 24, 1935 UNITED STATES WELDED BOILER DRUM Louis G. Haller,

Chattanooga,- Tenn., assignmto Combustion Engineering Company, Inc., New York, N. Y., a corporation of Delaware Application December 13, 1933, Serial No. 702,112 2 Claims. (01. 12 2-365) This invention relates to welded boiler drums for use in high pressure boilers.

In the construction of a' high pressure boiler drum in which a plurality of tubes are connected thereinto, a relatively thick wall must be employed in order to provide the efl'iciency of the tube ligaments necessary to withstand the pressure. Thus in the case of a solid seamless drum, even though a relatively thin shell would withstand the pressure in the absence of tubeholes, the shell thickness, because of the tube holes, must be substantially increased and this of course increases the weight and the cost of the drum.

It has been proposed heretofore to reduce the weight and cost by providing drums in which the portion at which no tube holes arelocated is thinner than the portion having tube holes and in which said portions are welded together. However, in no former construction of which I am aware was proper provision made at the welds to ensure adequate weld efiiciency with minimum shell thickness. For example, it has been customary in prior welded drums to make the thickness of the entire portion or section of the drum at which no tube holes are located, of the thickness necessary to ensure the requisite efficiency at the welds and to make the remaining portion or requisite tube ligament efliciency. While this results in some reduction in weight and "cost, I

I of improved construction requirements which is of and of low cost. How the foregoing, together with such other objects and advantages as may hereinafter appear, or are incident 'to my invention, are realized, is illustrated in preferred form in the accompanying drawing, wherein- Figure 1 is a fragmentary side elevation of a boiler drum embodying my improvements;

Figure 2 is a cross section taken on the line 2-2 of Figure 1;

adapted to fufill such relatively light weight "nfigure 3 IS an arms sectional mew g tube arrangement require. a plate thickness for a iragmentof the drum illustrated in Figure l;

and

Figure 4 is a view similar to Figure 3 but illustrating a modification of the invention. Referring to Figures 1 and 2 it will be seen that the drum 6 is composed of two arcuate portions pressures is provided.

the drum thicker so as to provide the or sections 7 and 8 welded together at their meeting edges, the welds being indicated by the reference numeral 9. The section 7 is provided with a multiplicity of tube holes ID for the reception of boiler tubes ll and the section 8 is free of such tube holes.

Since the section 1 is provided with tube holes it must be made of a thickness such that the ligament efficiency necessary to withstand the high However, the section 8 10 which is free of such tube holes may be made thinner and still withstand the pressure and thus the drum will be considerably lighter and of lower cost than if it were made entirely of the thickness required for the needed ligament efiiciency referred to;

It is to be observed, however, that since the drum is of .welded construction the matter of weld efficiency must also be taken into consideration, and this requires a plate or shell thickness greater than that necessary in a drum of solid seamless form under like pressure conditions. As pointed out above, this has been taken care of previously by making the entire section which is free or" tube holes, such as the section 8 of Figure 2, of the thickness required to obtain the needed weld efficiency. v

I have provided an arrangement whereby all of the boiler code requirements as to plate, weld and ligament efliciency, can be met in a. drum of still lighterweight and of less cost comprising a relatively thick arcuate section 7 and a relatively thin arcuate section 8, which sections have their end portions 52 and 13 so formed that the thickness of metal in the region of the welds is 35 such as will ensure the required weld efficiency. Since the section 2? is thicker and the section 8 thinner than needed for weld efiiciency, I reduce the thickness of the former at its longitudinal edges 52 and increase the thickness of the latter at its longtiu'dinal edges 13 to the-thickness required for weld emciency. The relative thickness of these sections or portions will be undenstood irom the following.

' Let us assume that a drum of 23 inches inside diameter is to be provided in accordance with my invention for a working pressure of 4-00 the length of the drum and of a width equal to the circumferential length of the arcuate secalignment with the mean circumferences of the sections are coincident.

In Figure 4 I have illustrated an arrangement in which there is a gradual increase in the thickness of the wall from the section I to the section 8, with the weld located approximately-centrally f the tapered portion. In this form it is preferable to have the taper at both tn..- outside and inside of the drum similar to Figure 3.

By having the neutral axes of all of the sections fall in the same circumferential line as above described, the tendency for the drum to become out of round each time pressure is set up therein is avoided. In this connection it is pointed out, for example, that if the thicker portion had its mean circumference outside that of the thinner portion, excessive stresses would be set up at the lines near-the junction of these portions, with the result that there would be a decided tendency to cause the drum to become out of round each time pressure is set up. therein, and this action would cause excessive fatigue stresses in the shell particularly near the welds.

This is due to the fact that when the mean circumferences or the center lines of the stresses of the sections are offset, as mentioned above, a

my invention a saving in weight is eflected equal to a plate .097 inch thick, of a length equal to turning movement is caused which increases the fiber stresses in the thinner section in the portion outside of the mean circumference, and this tends to throw the drum out of round in the region where the two sections join together.

Aside from the fact that the weight and cost of the drum is kept down by making the sections or portions of the drum at the weld only of the thickness necessary for an effective weld, the added advantage is obtained of keeping the 10 thickness at the weld such that it will be possible to make an X-ray examination of'the weld to determine its efiectiveness.

'I claim:--

1. A boiler drum comprising two arcuate secl5 tions weidedtogether at their meeting edges, one being relatively thick and the other relatively thin, said thick section having edge portions of reduced thickness but thicker than the thickness of the thin section and said thin section having edge portions of increased thickness corresponding to the thickness of the edge portions of the thick section, said thick and thin sections and the edge portions thereof being so relatively. disposed that the center line of the stresses thereof 5 lie in the. same circumferential line.

2. A welded boiler drum comprising a shell section freeof tube holes and of a thickness to be 100% efilcient for a given pressure, and a shell section having a plurality of tube holes and of a thickness greater than the first section to provide the ligament efiiciency necessary for said pressure, said sections having their edge portions of a thickness thicker than the first section and. thinner than the'second section to provide the efliciency necessary for said pressure at welds joining-the edge portions, said sections and their edge portions being arranged so that their mean circumferences are coincident.

LOUIS G. HALLER. 

